These files are skins....they allow you to use different appearances in Quake 2. You hit ESC when in the game then go to multiplayer and to player setup. Then you are able to switch between male/female/cyborg. These are the files in your baseq folder. You can then switch between the genders and then change the skin. They show a spinning model and the picture. Editing these are slightly difficult. I might put a tutorial or how-to on the quake 2 page.
To get other skins and .md2 files (the 3d figure under the skin... vary from character to character) go into multiplayer and player setup once more. This will make you see the stuff above and at the very bottom there will be a thing that says download options. Then just click it on or whatever!